JPH07328448A - Exhaust gas purification catalyst and device for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To efficiently remove NOx in a lean burning region or the region from a lean burning region to a stoichiometric (theoretical fuel-air ratio) region. CONSTITUTION:A transition metal such as Co, Cu or Ni and antimony are incorporated into zeolite to obtain an NOx catalyst 1 for lean burning and NOx is removed using this catalyst 1 from oxygen-contg. exhaust gas from an internal-combustion engine. The catalyst 1 for removal of NOx in a region above a stoichiometric region may be used in combination with a ternary catalyst 3 acting in a stoichiometric region or an adsorbent adsorbing NOx in a lean burning region and desorbing NOx in a stoichiometric region may be used in addition to the catalysts 1, 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion exhaust gas purifying catalyst and an exhaust gas purifying apparatus, and more particularly to a catalyst and an apparatus suitable for purifying nitrogen oxides.

[0002]

2. Description of the Related Art Exhaust gas emitted from an engine of an automobile or the like contains nitrogen oxides and the like, which are harmful to the human body and cause the destruction of the global environment such as acid rain. Therefore, various studies have been made on methods for purifying nitrogen oxides in exhaust gas.

Currently, in automobiles, the air-fuel ratio of the engine is set to a stoichiometric value, that is, near the stoichiometric air-fuel ratio (A / F = 14.6: the weight ratio of air A to fuel F), and the exhaust gas produced is made of precious metals (rhodium, palladium). , Platinum) is used as a three-way catalyst to reduce nitrogen oxides (NOx) to nitrogen, and hydrocarbons (HC) and carbon monoxide (CO) become carbon dioxide gas (CO).
Purified by oxidizing to ₂ ).

By the way, in recent years, regarding the automobile, the air-fuel ratio is set to the theoretical air-fuel ratio (14.
6) The lean burn engine as described above is being developed, and its spread is expected. However, in a lean burn engine, oxygen is excessively contained (at least 0.5% or more) in the exhaust gas as compared with the stoichiometric air-fuel ratio. Therefore, in the currently used three-way catalyst, O ₂ having a strong oxidizing power is CO, H.
By reacting with C, only the oxidation of HC and CO proceeds, and NOx, which has a weaker oxidizing power than O ₂ , does not react with CO and HC, and NO
The x reduction cannot be performed effectively.

On the other hand, diesel engines such as diesel automobiles are conventionally operated at a high air-fuel ratio with excess oxygen. Therefore, the above three-way catalyst cannot be applied, and the effective NO
I have not found a way to reduce x.

One of the NOx removal methods currently in practical use is the NH ₃ reduction method using a V ₂ O ₅ —TiO ₂ catalyst. In this method, even if a large amount of oxygen coexists in the exhaust gas, N
The feature is that Ox can be removed. However, this method uses NH ₃ , which is a harmful substance, and
Since it requires an H ₃ supply tank, it is difficult to use for mobile small engines such as automobiles.

Therefore, in recent years, much research has been conducted on a catalyst for purifying nitrogen oxides without using NH ₃ in an oxidizing atmosphere in the presence of excess oxygen. Among them, a method of removing NOx by utilizing HC and O ₂ contained in the exhaust gas has attracted attention.

At present, as such a catalyst, a catalyst in which copper is supported on zeolite [for example, JP-A-1-151706, 69th Symposium on Catalysis, 3F108 (199)
2)] or a catalyst containing cobalt, rare earth, copper and / or rhodium in zeolite (Japanese Patent Laid-Open No. 4-219147).

Further, by installing a catalyst in which La and Ba are contained in Al ₂ O ₃ and the three-way catalyst component Pt in the exhaust passage of an engine capable of lean combustion, NOx is emitted from the lean air condition to the stoichiometric ratio. Purification method (Japanese Patent Laid-Open No. 5-261)
No. 287) has been reported.

[0010]

However, the following problems remain in the above-mentioned method.

That is, the catalyst in which copper is supported on zeolite (JP-A-1-151706, etc.) exhibits an extremely high performance in a low temperature range due to the unique adsorption property of copper for nitrogen oxides, but exhibits a catalytic action. The temperature range (window) is narrow.

Therefore, as a catalyst for expanding the window, zeolite, cobalt, rare earth, copper,
Catalyst containing rhodium (Japanese Patent Laid-Open No. 4-219147)
Was proposed, and it became possible to purify nitrogen oxides in a relatively wide temperature range.

However, it is known that the catalyst in which copper is supported on zeolite has a low catalytic activity when a large amount of water coexists. Therefore, as a catalyst for purifying exhaust gas of an automobile engine whose exhaust gas contains water, higher nitrogen oxide purifying performance and water resistance are required.

A catalyst in which Al ₂ O ₃ contains La and Ba and Pt which is one of the three-way catalyst components (Japanese Patent Laid-Open No. 5-1
87229), it is reported that catalyst deterioration that prevents grain growth of Pt due to La oxide and Ba oxide to prevent reduction of active sites, promotion of Pt catalytic action and NOx storage. The NOx occlusion occurs lean, and in the vicinity of the theoretical air-fuel ratio, it reacts with CO and reducing agents such as HC and H ₂ and is released as N ₂ . The catalyst also removes NOx using Pt, which is a three-way catalyst component, even when lean, but it is generally considered that it is difficult to completely remove NOx in a low temperature range by a three-way reaction with Pt alone. Then, there seems to be room for further improvement.

The present invention has been made in view of the above points, and, firstly, an object thereof is in an exhaust gas containing a large amount of oxygen, such as in a lean combustion region of an engine (air-fuel ratio region larger than the theoretical air-fuel ratio). An object of the present invention is to provide an exhaust gas purifying catalyst that realizes NOx removal performance by guaranteeing water resistance (preventing performance deterioration due to water vapor in exhaust gas).

Secondly, it is to provide an exhaust gas purifying catalyst or device which has improved NOx removal performance in exhaust gas from the lean combustion region to the stoichiometric air-fuel ratio region.

Thirdly, to provide an exhaust gas purifying catalyst or device which improves the NOx removal performance in the exhaust gas from the lean combustion region to the stoichiometric air-fuel ratio region while achieving the miniaturization of the exhaust gas purifying device. It is in.

[0018]

[Means for Solving the Problems]

(1) In order to achieve the first object, basically,
As an exhaust gas purifying catalyst, a catalyst containing transition metal and antimony in zeolite is proposed (this is the first invention; corresponding to claims 1 to 6).

<Constituent Elements of the Invention> Zeolite is a crystal of aluminosilicate, and its chemical formula is Q _n Al _{n
Si n O n · mH 2 O} ( wherein Q is Na, Ca, K, B
At least one of a and Sr, Si / Al> 1, n is a numerical value indicating the number of each compositional element, and the numerical value n of each compositional element does not necessarily match, and m is a numerical value indicating the number of molecules). Further, SiO ₄ tetrahedron and AlO ₄ tetrahedron may have a skeleton structure in which O is shared in a sterically-bonded manner, and zeolite species having various different skeleton structures, for example, mordenite, ZSM-5, faujasite , X type, Y
Type and A type can be applied.

Zeolites include protons and sodium ions as substances that are preexisting at the ion exchange point, and they are referred to as H-type mordenite and Na-type ZSM-5 by distinguishing them. Is not limited by the surface exchange ionic species. In addition, part of Al and Si is P, V, Ti
It may be substituted with, for example, and an ion exchanger having a high specific surface area is particularly preferable. Due to this high specific surface area, active metals such as Cu, Ni, Co and Sb can be highly dispersed on the carrier. It has the property of exchanging metal ions with the aforementioned ion exchangers (cations such as protons and sodium ions), and it is possible to contain cobalt, copper, alkaline earth metal elements and rare earth metal elements as ion exchangers. . Generally, this exchange rate is higher as the silica / alumina ratio is smaller. By adding the following metal salt to this zeolite, a catalyst that meets the object of the present invention can be prepared.

The transition metals in the present invention are Cu, Ni, C
It is desirable that it consists of at least one of o.

The metal salts used in the above catalyst preparation are transition metal salts and antimony salts. These metal salts include nitrates, acetates, hydrochlorides, sulfates, carbonates, etc. It is not limited to the type of salt.

As the catalyst preparation method of the present invention, an ion exchange method, an impregnation method, a kneading method and the like can be applied. Further, as the order of containing the metal salt, a method of containing all of them in the zeolite at the same time, a method of containing each of them in the zeolite one by one, or the like can be applied. In the present invention, a method of preparing a catalyst by kneading a transition metal salt, an antimony salt, and a crystal of zeolite or aluminosilicate while adding water was preferable. The shape of the zeolite used for preparing the catalyst is arbitrary such as powder, granules, and honeycomb.

The content of antimony is preferably such that the antimony content is 0.1% by weight or more and 1.5% by weight or less with respect to 100% by weight of zeolite.
Regarding the content of transition metals, Al of zeolite
It is desirable that the number of atoms is 0.4 to 2 times that of one atom.

The catalyst precursor containing these metal salts in zeolite is dried at 100 ° C. or higher but lower than 150 ° C. for 1 hour or longer but shorter than 2 hours, and then dried at 300 ° C. or higher but lower than 750 ° C., preferably about 500 ° C. It is desirable to perform a baking treatment for about 2 hours.

The catalyst produced as described above may have any shape such as powder, granules, pellets, or honeycomb, and it can be used by supporting it on any porous carrier such as cordierite or metal honeycomb. .

The present catalyst can be applied to gases containing at least oxygen, hydrocarbons and nitrogen oxides, and can be applied to engine exhaust gases such as gasoline engine exhaust gas and diesel engine exhaust gas, and to these exhaust gases as necessary. Can be added for use. <Use conditions of the catalyst> Catalyst temperature: 100 ° C or higher and 800 ° C or lower, preferably 2
Oxygen concentration: 0.5% or more and 20% or less is desirable, and NOx concentration and HC concentration are 0.5 or more and 10 or less, preferably about 1 to 5 in terms of C / N atomic ratio. It is desirable to do.

<Aspects of Use> The catalyst having the above structure can be used alone or in combination with other types of catalysts depending on the intended use.

FIG. 1 shows an example of its use, wherein reference numeral 1 is the catalyst of the present invention (zeolite containing a transition metal and antimony; hereinafter also referred to as lean burning NOx catalyst), reference numeral 3 Is a three-way catalyst.

FIG. 1 (A) shows an example of single use of the catalyst 1 of the present invention, in which lean combustion NOx is provided in the exhaust passage 15 of the engine.
The catalyst 1 is installed (this is the first usage mode).

FIG. 1B shows the catalyst 1 of the present invention and the three-way catalyst 3.
It is a combination of and. This example of use is a case where it is necessary to remove HC and CO (oxidation removal) in a wide air-fuel ratio region in addition to NOx removal (NOx reduction) like exhaust gas purification of an automobile engine. In this case, the lean-burn NOx catalyst 1 of the present invention is installed between the engine and the three-way catalyst 3 in the exhaust passage 15 of the engine (this is the second usage mode).

As a modification of FIG. 1 (B), as shown in FIG. 1 (C), the exhaust gas may flow only to the three-way catalyst 3 by using, for example, the bypass 5 at the time of stoichiometry. In this case, the selection of the bypass 5 is performed by controlling the switching of the switching valve 4 by the stoichiometric detection (this is a third usage mode).

Further, as indicated by reference numeral 9 in FIG.
The lean-burn NOx catalyst and the three-way catalyst of the present invention are integrated (however, the lean-burn N of the present invention precedes the three-way catalyst).
The Ox catalyst needs to be arranged) and installed (this is the fourth mode of use).

(2) In order to achieve the above second object, the following is proposed.

This will be described with reference to the reference numerals of the examples of use in FIGS.

One is an exhaust gas purifying apparatus as shown in FIG.
As shown in (A), a lean-burn NOx catalyst 1 having nitrogen oxide removal performance in an air-fuel ratio region larger than the theoretical air-fuel ratio is installed in the exhaust passage 15 of the engine, and a theoretical stage is provided downstream of the catalyst 1. An adsorbent 2 capable of adsorbing nitrogen oxides in the air-fuel ratio region larger than the air-fuel ratio and releasing nitrogen oxides in the stoichiometric air-fuel ratio region is installed, and further, a three-way catalyst 3 is provided in the subsequent stage of the adsorbent 2. Installed (This is 2-1
The invention is defined as: (corresponding to claim 7). In addition,
As a modified example, as shown in FIG. 2 (B), when the engine burns in stoichiometry, the exhaust gas bypasses the lean-burn NOx catalyst 1 and has a bypass flow path 5 that flows to the adsorbent 2. Propose a thing (corresponding to claim 8).

The other is, as shown in FIG. 2C, the exhaust gas purifying catalyst 6 is a three-way catalyst component for removing nitrogen oxides in the exhaust gas at the theoretical air-fuel ratio of the engine, based on the theoretical air-fuel ratio. An adsorbent component capable of adsorbing nitrogen oxides in a large air-fuel ratio region and releasing nitrogen oxides in the theoretical air-fuel ratio region,
In addition, it is proposed to include a lean-burn NOx catalyst component having the ability to remove nitrogen oxides in a region equal to or higher than the stoichiometric air-fuel ratio (this is the invention of No. 2-2; corresponding to claim 9). In this case, the structure of the catalyst 6 is such that the porous honeycomb is coated with the component of the adsorbent 2, the layer of the component 3 of the three-way catalyst is coated thereon, and the component of the lean combustion NOx catalyst 1 is further coated thereon. A multilayer honeycomb coated with layers may be used (corresponding to claim 11). In addition, this coated product is described in a third invention to be described later.

Further, as a modification of these inventions, as shown in FIG. 3A, the three-way catalyst 3 is provided after the catalyst 7 containing the components of the adsorbent 2 and the NOx catalyst 1 for lean combustion. Is proposed (this is a second to third invention; corresponding to claim 14). In this case, when the combustion is stoichiometric, a bypass may be provided to bypass the catalyst 7 and guide the exhaust gas to the three-way catalyst 3 (corresponding to claim 15). Further, in connection with this, a layer of components of the adsorbent 2 and a lean combustion NOx catalyst 1 are formed on the porous honeycomb.
It is proposed to coat a layer of the above component (corresponding to claim 13).

Further, as shown in FIG. 3 (B), it is proposed that a catalyst 8 containing the components of the three-way catalyst 3 and the adsorbent 2 is installed in the latter stage of the lean-burn NOx catalyst 1 ( This is defined as a second to fourth inventions (corresponding to claim 16). In this case, the catalyst 8 may be composed of a multilayer honeycomb in which a layer of the component of the adsorbent 2 is coated on a porous honeycomb, and a layer of the component of the three-way catalyst 3 is coated on the porous honeycomb (corresponding to claim 17). . Further, as a modification thereof, at the time of stoichiometry, the lean combustion NOx catalyst 1 may be bypassed so that the exhaust gas flows through the catalyst 8 (this is referred to as a second to fifth inventions; claim 18). .

The NOx catalyst for lean combustion in the 2-1 to 2-5 inventions includes the one according to the first invention, but the gist of the invention is not limited to this.

(3) In order to achieve the third object,
Basically, the following problem solving means are proposed. This will be described with reference to the reference numerals of the embodiment of FIG.

First, as shown in FIG. 7 (a), a porous honeycomb 10A through which engine exhaust gas is passed is coated with a layer 13 of a three-way catalyst component for removing nitrogen oxides at a stoichiometric air-fuel ratio, Furthermore, lean combustion NO having the ability to remove nitrogen oxides in the air-fuel ratio region larger than the theoretical air-fuel ratio
An x-catalyst component layer 11 is coated to form an exhaust gas purification catalyst (this is referred to as a 3-1 invention; claim 10).

The other is, as shown in FIG. 7B, in the stoichiometric air-fuel ratio region, nitrogen oxides are adsorbed in the air-fuel ratio region larger than the stoichiometric air-fuel ratio to the porous honeycomb 10A through which the exhaust gas of the engine passes. A layer 12 of an adsorbent component that releases nitrogen oxides is coated, a layer 13 of a three-way catalyst component that removes nitrogen oxides at a stoichiometric air-fuel ratio is coated thereon, and a region larger than the stoichiometric air-fuel ratio is further coated thereon. The exhaust gas purifying catalyst is formed by coating the layer 11 of the lean-burn NOx catalyst component having the ability to remove nitrogen oxides with the above (this is the invention of claim 3-2; corresponding to claim 11).

Alternatively, in the third to third inventions, the layer arrangement is exchanged, and the three-way catalyst component layer 13 for removing nitrogen oxides at the stoichiometric air-fuel ratio is added to the porous honeycomb 10A through which the exhaust gas of the engine passes. And a layer 12 of an adsorbent component that adsorbs nitrogen oxides in the air-fuel ratio region larger than the stoichiometric air-fuel ratio and releases nitrogen oxides in the stoichiometric air-fuel ratio region, and further coats the stoichiometric air-fuel ratio An exhaust gas purifying catalyst is constituted by coating a layer 11 of a lean-burn NOx catalyst component having a capability of removing nitrogen oxides in a larger air-fuel ratio region (this is referred to as a third to third inventions; 12 correspondence).

The layer 11 of the NOx catalyst component for lean combustion includes the layer according to the first invention, but the gist of the present invention is not limited to this.

[0046]

[Action]

(1) Action of the first invention ... Transition metal (eg, Co, Cu, Ni, etc.) contained in zeolite (catalyst support),
N in the presence of antimony (Sb) in excess of O ₂ and HC
Although the reaction mechanism for Ox is not always clear, it is considered to exert the following effects.

The transition metal is a reaction field for reacting NOx with O ₂ and HC to reduce and remove N ₂ (NOx +
HC + O ₂ → N ₂ + H ₂ O + CO ₂ ), on the other hand, antimony suppresses the combustion of HCs in a low temperature range (suppressing the reaction consisting of HC + O ₂ → CO ₂ , CO, if this is represented by a chemical formula, It can be said that the effect of suppressing the decrease of HC due to the above NOx reaction) and a material for preventing water adsorption on the catalyst (water repellency). However, it is not always necessary that all transition metals and antimony be ion-exchanged.

By the above action, NOx can be purified even in the presence of excess O ₂ with a window in the temperature range widened and hardly affected by water vapor.

Among the usage examples of the first invention, usage mode 1 (FIG. 1 (A)) is the same as that of the first invention, and therefore, particularly in the lean combustion region (from the theoretical air-fuel ratio). N in a large air-fuel ratio region with O ₂ excess and HC coexistence)
Ox purification (reduction removal to N ₂ ) can be achieved.

Usage Modes 2 to 3 [FIG. 1 (B) to FIG.
In (D)], during lean combustion, NOx is reduced and reduced by reacting NOx with HC and O ₂ by the lean-burn NOx catalyst 1 of the present invention.
NOx is purified by the reaction between CO and NOx. At this time, it goes without saying that HC and CO are also purified by the oxidation reaction with NOx and O ₂ .

(2) Action of the 2-1 invention During lean combustion (air-fuel ratio range larger than stoichiometric air-fuel ratio),
NOx in the exhaust gas reacts with HC and O ₂ exclusively through the lean-burn NOx catalyst 1 to remove (reduce) to some extent.
The NOx that has been removed and not removed is adsorbed by the adsorbent 2 at the next stage, and the NOx discharged to the outside air can be greatly reduced.

In the stoichiometric (theoretical air-fuel ratio range) state, CO, HC and NOx in the exhaust gas react with each other by the catalytic action mainly by the three way catalyst (for example, noble metal: rhodium, palladium, platinum) 3. It is discharged as CO ₂ , H ₂ O, and N ₂ , but in this case, the NO adsorbed on the adsorbent 2
x is also released to the three-way catalyst (desorption of NOx) and is reduced and removed to N ₂ . An oxide or a composite oxide composed of La and Ba has the characteristics of the adsorbent 2.

As a result, NOx from lean to stoichiometric
Can be removed efficiently.

In the present invention, the three-way catalyst is arranged downstream of the lean-burn NOx catalyst. However, when the three-way catalyst is arranged in the opposite direction, the amount of HC required for the NOx reduction reaction during lean combustion is reduced to three. Since the NOx for lean combustion cannot be effectively worked because it is removed by the original catalyst, it is necessary to comply with the arrangement of the present invention.

The function of the second to second inventions ... In the present invention, the components of the lean combustion NOx catalyst 1, the adsorbent 2 and the three-way catalyst 3 as in the above 2-1 invention are stored together. This is summarized in Fig. 2 (C).
In the present invention, the same operation as the above 2-1 invention can be performed. In addition, 2-3 to 2-
In the fifth aspect of the invention, the same operation as that of the second aspect of the invention is performed.

(3) Action of the 3-1th invention: NOx catalyst component for lean combustion provided on the side wall of each gas passage hole 14 in the process in which engine exhaust gas passes through each hole 14 of the porous honeycomb 10A. Layer 11 and the three-way catalyst component layer 13 are permeated. Therefore, the NOx at the time of lean combustion is H which is the other exhaust component in the layer 11 of the NOx catalyst component for lean combustion.
It reacts with C, O _2, etc. and is reduced to N ₂ . At the time of stoichiometry, CO, HC, and NOx in the exhaust gas are controlled by the three-way catalyst
React with each other by a catalytic action and are discharged as CO ₂ , H ₂ O and N ₂ . Moreover, according to the present invention, the NOx catalyst 11 for lean combustion and the layer 13 of the three-way catalyst component can be coated on the porous honeycomb 10A in a laminated form to be integrated, so that the exhaust gas purifying catalyst can be made compact. Can be realized.

Action of the 3-2nd invention: lean combustion NO provided on the side wall of each gas passage hole 14 in the process of the engine exhaust gas passing through each hole 14 of the porous honeycomb 10A.
The catalyst component layer 11, the three-way catalyst component layer 13, and the adsorbent layer 12 are permeated.

During lean combustion (air-fuel ratio region larger than the theoretical air-fuel ratio), the NOx catalyst layer 11 for lean combustion is exclusively used.
The NOx in the exhaust gas reacts with HC and O ₂ through the catalyst to be removed (reduced) to some extent, and the NOx that has not been removed passes through the three-way catalyst layer 13 and is adsorbed by the adsorbent layer 12 to release the outside air. It is possible to significantly reduce the NOx discharged to.

In the stoichiometric (theoretical air-fuel ratio range) state, CO, H in the exhaust gas is mainly formed by the layer 13 of the three-way catalyst component.
C and NOx react with each other by a catalytic action to produce CO ₂ , H ₂
It is discharged as O and N ₂ , but in this case, layer 1 of the adsorbent
The NOx adsorbed on 2 is also released (NOx desorption) to the three-way catalyst and reduced and removed to N ₂ .

In the present invention, in order to function the layer 11 of the lean-burn NOx catalyst, it is arranged in the outermost layer, and after that, the three-way catalyst component layer 13 and the adsorbent component layer 12 are arranged. Need to be placed.

Also in the present invention, N for lean combustion is used.
Since the porous honeycomb can be coated with the Ox catalyst 11, the three-way catalyst component layer 13, and the adsorbent component layer 12 in a laminated form, the exhaust gas purification catalyst can be miniaturized.

In the 3rd to 3rd inventions, mechanically, the same operation as that of the 3rd to 3rd inventions is performed.

[0063]

EXAMPLES Examples of the present invention will be specifically described below.

Example 1 H-type ZSM-5 [SiO ₂ /
Al ₂ O ₃ molar ratio: 50, Na ₂ O: 0.02 wt (weight)%] 100 parts by weight, copper: 2.0 wt%, nickel: 1.5 wt% are contained, and further shown in Table 1. Example catalysts (1) to (6) were prepared so that the antimony concentration was obtained.

For example, in the case of the example catalyst (1) in Table 1, 30 g of the H-type ZSM-5 powder, 2.3 g of crystals of copper nitrate trihydrate, and 2.2 crystals of nickel nitrate hexahydrate.
g and 0.06 g of crystals of antimony trichloride were added, and the mixture was kneaded with a muller. Subsequently, distilled water was added thereto, and the mixture was kneaded for about 15 minutes until the dry mixture turned into a paste. After drying the paste at about 100 ° C. for about 2 hours, about 5
Bake at 00 ° C. Then, it is naturally cooled to room temperature. This powder catalyst was pressure-molded to a particle size of 1 mm or more and less than 2 mm to obtain a test catalyst.

[0066]

[Table 1] Comparative Example 1 H-type ZSM-5 was exactly the same as in Example 1 except that antimony trichloride was not added, and copper: 2.0 wt% and nickel: 1.5 wt per 100 parts by weight.
% Comparative catalyst (1) was prepared.

[Experimental Example 1] Catalyst (1)-
A nitrogen oxide (NOx) purification performance test was conducted on (6) and Comparative Example catalyst (1) under the following conditions. 3 cm catalyst
³ was filled in a Pyrex reaction tube. This is heated from the outside by an electric furnace to 150 ° C., then a reaction gas is circulated to raise the temperature to 600 ° C. at a rate of 10 ° C./m,
The reaction was carried out.

The reaction gas was NO: 1000 ppm, C ₃
H _8: 1000ppm, oxygen: 10%, nitrogen: and the rest were distributed as a space velocity of 60,000h ~ ^1.
The concentration of NOx purified by the above operation was measured by chemical spectroscopy.

Table 2 shows the catalyst layer inlet temperature of 200 to 500.
The average purification rate (average removal rate) at ° C is shown.

Example catalysts (1) to (5) are comparative example catalysts 1.
Although the NOx average purification rate was equal to or higher than, the Example catalyst (6) was inferior to the Comparative catalyst 1. In addition, by containing antimony, the maximum purification rate was decreased as compared with the comparative catalyst (1), but the maximum purification rate temperature was shifted to the high temperature side (this will be described in Table 3 below). . Moreover, the average purification rate is almost improved as compared with the comparative example catalyst, and the example catalyst removes NOx on average from the low temperature region to the high temperature region.

Here, the purification rate is the removal rate of NOx at the outlet with respect to the catalyst layer inlet, calculated according to the following equation, and the average purification rate is the average value of the purification rates at the catalyst layer inlet temperature of 200 ° C. or more and 500 ° C. or less.

[0072]

[Equation 1]

[0073]

[Table 2] "Experimental Example 2" Exactly the same experiment as in Experimental Example 1 was conducted to measure the removal of hydrocarbons (HC).

Table 3 shows the catalyst layer inlet temperature of 300 ° C to 400 ° C.
The HC removal rate at ° C was shown. Antimony acts as a combustion suppressing effect agent for HC. Here, the HC removal rate was calculated according to the following equation.

[0075]

[Equation 2]

[0076]

Table 3 Table 3 Catalyst HC removal rate (%) 300 ° C. 350 ° C. 400 ° C. Example catalyst (1) 80 100 100 Example catalyst (2) 78 100 100 100 Example catalyst (3) 75 100 100 Example catalyst (4) 72 94 100 Example catalyst (5) 65 75 100 Example catalyst (6) 63 73 100 Comparative example catalyst (1) 80 100 100 As is clear from the experimental data in Table 3, the example catalyst ( 1) -Example catalyst (6), 300 ℃, 350 ℃
The HC removal rate decreases in the temperature range of. This is NO
When x is present in the atmosphere, it means that there is a large amount of HC that serves as a reducing agent for NOx. It can be understood from this that the maximum purification rate temperature of NOx shifts to the high temperature side, HC is secured in a wide temperature range, and NOx purification is promoted. That is, antimony acts as a HC combustion suppression (oxidation suppression) effect agent.

Example 2 In the above Example 1, ZS
M-5 is an H-type ZSM with a SiO ₂ / Al ₂ O ₃ molar ratio of 80
Except for changing to 5 zeolite (Na ₂ O: 0.05 wt%), the same procedure was performed as in Example 4 except that the antimony concentration shown in Table 4 was prepared.

[0078]

[Table 4] "Comparative Example 2" In Example 2, a comparative catalyst (2) containing no antimony was prepared.

"Experimental Example 3" Catalysts (7) to (1)
The NOx removal rate of 2) and the catalyst of Comparative Example (2) were evaluated in exactly the same manner as in Experimental Example 1. The results are shown in Table 5.

[0080]

[Table 5] Example 3 The catalyst preparation method was the same as in Example 1, except that ZSM-5 was replaced with H-type mordenite having a SiO ₂ / Al ₂ O ₃ molar ratio of 16, and H, mordenite was replaced with Co, Cu,
Example catalysts containing Ni and Sb (1
3) to (17) were prepared. "-" In the table indicates that the containing operation was not performed. For Co, Cu, and Ni, catalyst preparation is performed using crystals of nitrate.

Comparative Example 3 Comparative example catalyst (3) was prepared in the same manner as in Example 4 except that antimony was not added.
~ (7) was prepared. It is shown in Table 6 together with the example catalysts.

[0082]

Table 6 Table 6 Content (wt%) Co Cu Ni Sb Example catalyst (13) 2-4 0.2 Comparative example catalyst (3) 2-4- Example catalyst (14) 2 2-0. 2 Comparative catalyst (4) 2 2 − − Example catalyst (15) 4 − − 0.2 Comparative example catalyst (5) 4 − − − Example catalyst (16) − 4 − 0.2 Comparative example catalyst (6) ) -4--Example catalyst (17)-3 0.2 Comparative example catalyst (7)-3-"Experimental example 4" The above-mentioned example catalysts (13) to (17) and comparative example catalyst (3) In (7) to (7), the NOx removal rate was evaluated in the same manner as in Experimental Example 1. The results are shown in Table 7.

[0083]

[Table 7] "Experimental Example 5" Using Example catalyst (3), Example catalyst (8) and Comparative example catalysts (1) and (2)
The NOx removal rate was evaluated by the same method except that 0 wt% was added. The results are shown in Table 8. "-" Indicates that no steam was added. It can be seen that the catalyst added with antimony is less affected by water vapor.

[0084]

Table 8 Catalyst Catalyst Water vapor concentration (%) NOx average removal rate (%) Example catalyst (3) -52 Example catalyst (3) 1050 Example catalyst (8) -48 Example catalyst (8) 10 46 Comparative catalyst (1) − 46 Comparative catalyst (1) 10 23 Comparative catalyst (2) − 40 Comparative catalyst (2) 10 24 Therefore, among the example catalysts, the example catalysts (1) to ( 1
According to 7), the NOx purification effect at the time of lean combustion (air-fuel ratio range larger than the theoretical air-fuel ratio) can be enhanced, and further, the deterioration of NOx purification performance due to water vapor can be prevented.

FIG. 5 shows an example in which the lean combustion NOx catalysts of (Example 1) to (Example 3) are applied to an exhaust gas purifying catalyst device of an automobile engine (lean burn system specification vehicle or diesel engine vehicle). . This application example
This corresponds to the usage mode of FIG. 1A, and the lean combustion NOx catalyst 1 is installed in the exhaust gas flow path 15,
The lean-burn NOx catalyst 1 is prepared by containing a transition metal and antimony in zeolite, and has a porous honeycomb shape. Reference numeral 14 is each exhaust gas circulation hole. Alternatively, the catalyst may be supported on cordierite or a metal honeycomb.

The catalysts (1) to (17) of the above examples
By combining the above catalyst and the three-way catalyst, NOx can be removed in a wide range from lean to stoichiometric.
The effect of that example has been confirmed in Experimental Example 6 below.

"Experimental Example 6" A three-way catalyst was placed after the example catalyst (8). The catalyst amount was set to 3 cm ³ and filled in a Pyrex reaction tube. Each was heated from the outside by an electric furnace to 150 ° C., and then a reaction gas was circulated to raise the temperature to 600 ° C. at a rate of 10 ° C./m to carry out the reaction.

When the lean model gas was used, the example catalyst (8) and the three-way catalyst were circulated, and when the stoichiometric model gas was used, only the three-way catalyst was circulated. The reaction gas is lean model gas, NO: 0.6%,
_{C 3 H 6: 0.04%,} CO: 0.1%, CO 2: 10
%, O ₂ : 4%, steam 10%, nitrogen balance 300
0 cc / m, NO: 0.1 as stoichiometric model gas
%, C ₃ H ₆ : 0.05%, CO: 0.6%, O ₂ : 0.
6%, steam 10%, nitrogen balance 3000cc / m
Was used. The concentration of NOx purified by the above operation was measured by chemical spectroscopy. No effect with lean gas
The average removal rate of x was about 48%, and that of stoichiometric gas was almost 100%.

This experimental example corresponds to the use mode of FIGS. 1B to 1D, and FIG. 6 is a more specific version of FIG. 1B.

In FIG. 6, both the lean combustion catalyst 1 and the three-way catalyst 3 according to the present invention are formed in a honeycomb shape, and the catalyst 1 is installed in the front stage of the exhaust passage 15 and the three-way catalyst 3 is installed in the rear stage thereof. Then, the exhaust gas purifying device is configured.

"Experimental Example 7" This experimental example is shown in FIG.
In the experiment of the usage mode of (B), the example catalyst (8) was used as the lean-burn NOx catalyst 1, the LaBa-based oxide was selected as the adsorbent 2, and the three-way catalyst 3 was also used.
The NOx catalyst 1 for lean combustion, the adsorbent 2, and the three-way catalyst 3 are sequentially installed in the exhaust flow path 15 from the front side. During lean combustion (when the air-fuel ratio is higher than the theoretical air-fuel ratio), NOx in the exhaust gas is reduced to H by the lean-burn NOx catalyst 1.
NOx is purified by reacting with C and O _2, and NOx that has not been reduced is adsorbed by the adsorption member 2. HC, CO, NO in exhaust gas by three-way catalyst during stoichiometry
In addition to the reaction of x, the NOx released from the adsorption member 2 also reacts.

Experiments were carried out in the same reactor as in Experimental Example 1. Example catalyst (8), LaBa-based oxide, and three-way catalyst honeycomb volume were each set to 3 cm ³ . The reaction method was as lean model gas: NO: 0.6%, C ₃ H ₆ : 0.04
%, CO: 0.1%, CO ₂ : 10%, O ₂ : 4%, steam 10
%, Nitrogen balance 3000 cc / m, as stoichiometric model gas, NO: 0.1%, C ₃ H ₆ : 0.05%, C
O: 0.6%, O ₂ : 0.6%, steam 10%, nitrogen balance of 3000 cc / m was used, and after passing the lean model gas at 300 ° C. for 3 minutes, the stoichiometric model gas was heated at 300 ° C. Allowed to flow for 3 minutes. The results are shown in Fig. 4.

In FIG. 4, the solid line indicates NO before entering the catalyst.
x concentration, the one-dot chain line indicates the NOx concentration at the catalyst outlet when the example catalyst (8) is used as the catalyst 1, and the dotted line indicates the catalyst outlet when the example catalyst (8) + adsorbent 2 + three-way catalyst 3 is used. The NOx concentration is shown, and the dotted line shows the adsorption effect during lean combustion.

Example 4 L was added to cordierite honeycomb.
70 g of aBa-based oxide is wash-coated with 100 g / l
After calcination at 0 ° C for 2 hours, 100 g / l of the three-way catalyst component was added.
Calcination was carried out at 900 ° C. for 2 hours, and the catalyst (8) of Example was wash-coated at 100 g / l.
The catalyst of Example (13) was produced by firing at 00 ° C. for 2 hours.

An example of this is shown in FIG. 7B. Reference numeral 10A corresponds to a cordierite honeycomb, 12 is a layer of an adsorbent component (LaBa oxide), 13 is a three-way catalyst layer, and 11 is a layer. NOx catalyst for lean combustion [Example catalyst (1
3)]. 14 is an exhaust gas flow hole.

"Experimental Example 8" In this example, FIG.
The experiment was conducted according to the usage mode of (C). The experimental method was exactly the same as in Experimental Example 5. The effect is similar to that shown by the dotted line in FIG. 4, and an effect of purifying exhaust gas such as NOx in a wide air-fuel ratio range can be obtained, and further, the size of the entire purifying device can be reduced.

FIG. 7 (a) is a modified example of Example 4, in which a cordierite porous honeycomb 10A is provided with a three-way catalyst layer 12, a lean combustion NOx catalyst [Example catalyst (1
3)] is coated to form the catalyst device 10.

Example 5 An Example catalyst (14) was prepared in the same manner as in Example 5, except that the three-way catalyst component was not coated.

Example 6 An example catalyst (15) was prepared in the same manner as in example 6, except that the example catalyst (8) was not coated.

[Experimental Example 9] FIG.
Experiments were conducted according to the usage patterns of (A) to FIG. 3 (C). The experimental method was exactly the same as in Experimental Example 5. The effect is Figure 4
Was the same as that indicated by the dotted line.

[0101]

【The invention's effect】

(1) According to the first invention, NOx can be purified from exhaust gas in an oxygen excess atmosphere with higher efficiency than in the conventional method. Therefore, it becomes possible to purify NOx over a wide range, such as combustion exhaust gas from consumer products such as automobile engines and cookware, and industrial combustion exhaust gas emitted from boilers of factories and thermal power plants. .

(2) According to the second aspect of the present invention, harmful components such as NOx in exhaust gas from a lean combustion region to a stoichiometric region, such as an automobile engine, can be purified with high efficiency.

(3) According to the third invention, the effect of the above (2) can be realized by a downsized purifying device.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of usage of a catalyst according to the present invention.

FIG. 2 is an explanatory view showing an example of usage of the catalyst according to the present invention.

FIG. 3 is an explanatory view showing an example of usage of the catalyst according to the present invention.

FIG. 4 is an explanatory diagram showing effects of the present invention.

FIG. 5 is an explanatory diagram showing an example in which the catalyst according to the present invention is applied to an exhaust gas purifying apparatus for an engine.

FIG. 6 is an explanatory view showing an example in which the catalyst according to the present invention is applied to an exhaust gas purifying device for an engine.

FIG. 7 is an explanatory view showing an example in which the catalyst according to the present invention is applied to an exhaust gas purifying apparatus for an engine.

[Explanation of symbols]

1 ... NOx catalyst for lean combustion, 2 ... adsorbent material, 3 ... three way catalyst, 4 ... bypass switching valve, 5 ... bypass passage, 10
... Catalyst, 10A ... Porous honeycomb, 11 ... NOx component coat layer for lean combustion, 12 ... Adsorbent component coat layer,
13 ... Coat layer of three-way catalyst component.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location B01J 35/04 ZAB A 331 A F01N 3/08 ZAB A 3/24 ZAB E 3/28 ZAB 301 C F02D 35/00 301 G B01D 53/36 102 D 104 A (72) Inventor Noriko Watanabe 7-1-1 Omika-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Akira Kato Ibaraki Hitachi City Omika-cho 7-1-1, Hitachi Co., Ltd. Hitachi Research Laboratory (72) Inventor Hiroshi Miyadera Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi 1-1, Inc. Hitachi Research Laboratory (72) Inventor Yuichi Kitahara 2520 Takaba, Katsuta-shi, Ibaraki Hitachi Ltd. Automotive Equipment Division (72) Inventor Hirotsuka Tokuda Ibaraki 2520 Takaba, Katsuda City, Castle Prefecture, Hitachi Automotive Systems Division, Hitachi, Ltd.

Claims (18)

[Claims] 1. An exhaust gas purification catalyst comprising zeolite containing a transition metal and antimony. 2. A chemical _{formula, Q n Al n Si n O} n · mH 2 O
(Here, Q is at least one of Na, Ca, K, Ba, and Sr, Si / Al> 1, n is a numerical value indicating the number of each composition element, and the numerical value n of each element does not necessarily match, m is a numerator The exhaust gas purifying catalyst is characterized by comprising a transition metal and antimony in an aluminosilicate crystal consisting of (a numerical value indicating the number). 3. The exhaust gas purifying catalyst according to claim 1, wherein the transition metal is made of at least one of Co, Cu, and Ni. 4. The exhaust gas purifying catalyst according to claim 1, wherein the antimony content satisfies the condition of 0.1% by weight or more and 1.5% by weight or less. . 5. An exhaust gas purifying apparatus, which removes nitrogen oxides from an exhaust gas containing oxygen of an engine using the exhaust gas purifying catalyst according to claim 1. Description: 6. The exhaust gas purifying catalyst according to claim 1, which is installed in an exhaust passage of an engine, between the engine and the three-way catalyst, or integrated with the three-way catalyst. An exhaust gas purifying device characterized by being installed. 7. A lean-burn NOx catalyst having nitrogen oxide removal performance in an air-fuel ratio region greater than the stoichiometric air-fuel ratio is installed in the exhaust passage of the engine, and an air-fuel ratio greater than the stoichiometric air-fuel ratio is provided in the latter stage of the catalyst. Characterized in that an adsorbent capable of adsorbing nitrogen oxides in the region and releasing nitrogen oxides in the stoichiometric air-fuel ratio region is installed, and further a three-way catalyst is installed in the latter stage of the adsorbent. Exhaust gas purification device. 8. A bypass passage, wherein exhaust gas bypasses the lean-burn NOx catalyst and flows to the adsorbent when the engine burns in a stoichiometric air-fuel ratio range. Exhaust gas purification device described. 9. A three-way catalyst component for removing nitrogen oxides in exhaust gas at a stoichiometric air-fuel ratio of an engine, which adsorbs nitrogen oxides in an air-fuel ratio region larger than the stoichiometric air-fuel ratio and removes nitrogen oxides in the stoichiometric air-fuel ratio region. An exhaust gas purification catalyst comprising an adsorbent component capable of being released, and a lean-burn NOx catalyst component capable of removing nitrogen oxides in an air-fuel ratio region larger than the theoretical air-fuel ratio. 10. A porous honeycomb that allows exhaust gas of an engine to pass through is coated with a layer of a three-way catalyst component for removing nitrogen oxides at a stoichiometric air-fuel ratio, and further coated with nitrogen in an air-fuel ratio region larger than the stoichiometric air-fuel ratio. An exhaust gas purifying catalyst, characterized by being coated with a layer of a lean-burn NOx catalyst component having the ability to remove oxides. 11. A layer of an adsorbent component that adsorbs nitrogen oxides in an air-fuel ratio region higher than the stoichiometric air-fuel ratio and releases nitrogen oxides in the stoichiometric air-fuel ratio region is coated on a porous honeycomb through which engine exhaust gas passes. , A NOx for lean combustion having the ability to coat a layer of a three-way catalyst component that removes nitrogen oxides at the stoichiometric air-fuel ratio, and further to remove nitrogen oxides in the air-fuel ratio region larger than the stoichiometric air-fuel ratio. An exhaust gas purification catalyst characterized by being coated with a layer of a catalyst component. 12. An engine exhaust gas-permeable porous honeycomb is coated with a layer of a three-way catalyst component that removes nitrogen oxides at a stoichiometric air-fuel ratio, and nitrogen oxidation is performed thereon in an air-fuel ratio region larger than the stoichiometric air-fuel ratio. NOx for lean combustion, which has the ability to adsorb substances and release nitrogen oxides in the stoichiometric air-fuel ratio region, and further to remove nitrogen oxides in the air-fuel ratio region larger than the theoretical air-fuel ratio. An exhaust gas purification catalyst characterized by being coated with a layer of a catalyst component. 13. An adsorbent component capable of adsorbing nitrogen oxides in an air-fuel ratio region larger than the stoichiometric air-fuel ratio and releasing nitrogen oxides in the stoichiometric air-fuel ratio region on a porous honeycomb through which exhaust gas of an engine passes. An exhaust gas purifying catalyst comprising a layer and a layer of a NOx catalyst component for lean combustion which has a property of removing nitrogen oxides in an air-fuel ratio region higher than the theoretical air-fuel ratio. 14. A layer of an adsorbent component capable of adsorbing nitrogen oxides in an air-fuel ratio region larger than the stoichiometric air-fuel ratio and releasing nitrogen oxides in the stoichiometric air-fuel ratio region in an exhaust passage of an engine, and a layer thereof. A porous honeycomb coated with a layer of a lean-burn NOx catalyst component having the ability to remove nitrogen oxides in an air-fuel ratio region larger than the stoichiometric air-fuel ratio is installed on the top, and a three-way catalyst is installed in the latter stage of this porous honeycomb. An exhaust gas purifying device characterized by being installed. 15. The exhaust gas according to claim 14, further comprising a bypass passage through which exhaust gas bypasses the porous honeycomb and flows to a subsequent stage when the engine burns in a stoichiometric air-fuel ratio range. Gas purification device. 16. A lean-burn NOx catalyst having nitrogen oxide removal performance in an air-fuel ratio region larger than the stoichiometric air-fuel ratio is installed in an exhaust passage of an engine, and a three-way catalyst is provided at a stage subsequent to the lean-burn NOx catalyst. A three-way catalyst with an adsorbent containing components and an adsorbent component capable of adsorbing nitrogen oxides in the air-fuel ratio region larger than the theoretical air-fuel ratio and releasing nitrogen oxides in the stoichiometric air-fuel ratio region is installed. An exhaust gas purification device characterized by being formed. 17. A lean-burn NOx catalyst having nitrogen oxide removal performance in an air-fuel ratio region larger than the stoichiometric air-fuel ratio is installed in an engine exhaust flow path, and the stoichiometric air-fuel ratio is provided in a stage subsequent to the lean-burn NOx catalyst. Porous having a layer of an adsorbent component capable of adsorbing nitrogen oxides in a larger air-fuel ratio region and releasing nitrogen oxides in a stoichiometric air-fuel ratio region, and a layer of a three-way catalyst component coated thereon An exhaust gas purification device comprising a honeycomb installed. 18. A bypass passage, wherein exhaust gas bypasses the lean-burn NOx catalyst and flows to a subsequent stage when the engine burns in a stoichiometric air-fuel ratio range. The exhaust gas purification device according to claim 17.